1. Technical Field
The present invention relates to a flash fixing device that fixes a toner image transferred onto a recording medium with light flashes irradiated from flash lamps, to an image forming device that uses this flash fixing device, and to a method for controlling light emissions from flash lamps.
2. Related Art
In an image forming device that forms images using an electrophotographic system, toner images formed from powdered toner are transferred onto a recording medium. After that, heat energy is applied to the recording medium to which the toner image was transferred (i.e., to the powdered toner on the recording medium), and the toner image is fixed on the recording medium by fusing the powdered toner. The heat energy for fixing the toner image is often supplied using heat rollers, however, flash fixing systems are used in high-performance image forming devices that can form mass amounts of images at high speed (e.g., in image forming devices that can form images on 500 sheets of recording medium equivalent to A4 per second). In a flash fixing system, powdered toner is fused by intermittently illuminating flash lamps and irradiating the light emitted from the flash lamps, whereby energy that fixes the toner image is supplied. Flash fixing systems are well-suited to high-speed image formation because high energy can be supplied without contact with the recording medium, hence, conveying of the recording medium is not adversely affected.
High-performance image forming devices have for the most part been applied to monochromatic ledger sheet printing. Nonetheless, even in ledger sheet printing, there are cases where the user wishes to print in color, for example, when adding a corporate logo to the header or footer of the ledger sheet. There is an ever-increasing need to improve upon color printing for high-performance image forming devices. Formation of color images with electrophotographic systems is performed by overlaying toner images of each color C (cyan), M (magenta), Y (yellow) (and K (black)). With this, the amount of toner transferred to the recording medium increases (i.e., the amount of toner to be fixed), whereby it becomes necessary to supply greater energy in order to fix the toner image.
In flash fixing systems, increases in the supplied energy can be achieved by lowering the speed by which the recording medium is conveyed (e.g., if the conveying speed is reduced by one half, twice as much energy is supplied) or by shortening the light emission cycles of the flash lamps (e.g., if the light emission cycle is made one half (i.e., the light emission frequency number is doubled) then twice as much energy is supplied). However, decreasing the conveying speed of the recording medium is not preferable because this results in the processing capability decline of the image forming device. Also, shortening the light emission cycles of the flash lamps is problematic in that the life of the flash lamps shortens and rises in the lamp temperature also increase. Further, if the number of flash lamps is increased, the supplied energy can be increased without reducing the conveying speed or shortening the light emission cycle. However, if a large amount of energy is supplied all at once, the toner composition sublimates (i.e., water included in the toner), whereby there might be cases where image deterioration such as dot patches (i.e., white points) occurs.